Field of the Invention
The present invention relates to a toner used in image forming processes such as electrophotography, electrostatic recording, or a toner jet process, and to a process for producing the toner.
Description of the Related Art
A technique of visualizing image information via an electrostatic latent image, e.g. electrophotography, is widely used in various fields including a copying machine, a printer, and the like. In recent years, in addition to higher image quality, there are also demands for other added values such as reduction in the size and cost of a device. To achieve stable image density or stable tinge by an electrophotography mode, it is necessary to establish, in continuous fashion, a constant development condition for a development process. If there is an occurrence of an image fogging by which a toner is developed in a non-image part, in particular, this would be recognized as a decrease in image quality. Furthermore, as the toner consumption amount also increases, it is disadvantageous in terms of reduction in the size and cost of a device.
It is considered that eliminating the occurrence of fogging completely, i.e. having absolutely no toner developed in a non-image part, is an extremely difficult matter to achieve. Meanwhile, it is possible to reduce the fogging to a certain level at which the fogging is visually not recognizable. In this respect, various suggestions have conventionally been made in relation to means for suppressing fogging, and those techniques are basically means for reducing the fogging to a level at which the fogging is visually not recognizable. There are roughly two ideas related to suppression of fogging, one being based on potential control of a development system, and the other being based on charge quantity control of a toner.
First, explanations are given for the potential control of a general development system. In an image part, the toner is carried on a toner carrying member while it is charged either positively or negatively. Furthermore, in an image part, whether the toner is transferred onto an electrostatic image bearing member or stays on a toner carrying member is decided based on the potential of an electrostatic image bearing member, potential of a toner carrying member, and charge quantity of a toner. Here, by creating a difference between the potential of a toner carrying member and the potential of an electrostatic image bearing member of a non-image part, control is implemented such that the toner is prevented from being developed in a non-image part to the maximum possible extent. This potential difference is expressed with various terms such as fogging-removing potential, Vback potential, and back contrast. In the present specification, the term back contrast will be applied. Currently, while it is most probable that high image quality can be achieved in various environments by finely setting the back contrast control, this would also lead to the inevitable disadvantage of the potential control devices becoming more and more complicated. This being the case, there is demand for a toner with which fogging can be suppressed in a broad back contrast range.
Next, explanations are given with regard to control of toner charge quantity. The main reason for having undesired development of a toner in a non-image part results from the presence, in each particle of a toner, of a particle with insufficient charge quantity, or the presence therein of a particle which is charged to have reverse polarity to that of the image concept. A toner with insufficient charge quantity has a rather insensitive response to back contrast and, either statistically or based on an action of adhesion forces other than electrostatic force, it is thus transferred to a non-image part. Accordingly, a toner charged to have reverse polarity to the image concept is actively developed in a non-image part. To achieve a toner in which those inappropriate particles are suppressed as much as possible, various techniques relating to toner have been suggested.
As a control for charge quantity of a toner, a control based on a charge control agent is mainly employed, and suggestions have also been made for a toner containing a calixarene compound, a toner containing an azo dye which includes iron, a toner using an organoboron compound, or the like (for example, Japanese Patent Application Publication No. 2002-287429 and Japanese Patent Application Publication No. 2004-219507).